In a process for producing an olefin compound, a fluid stream containing a saturated hydrocarbon such as ethane, propane, butane, pentane, naphtha, or mixtures of two or more thereof is fed into a thermal (or pyrolytic) cracking furnace. A diluent fluid such as steam is usually combined with the hydrocarbon feed material being introduced into the cracking furnace. Within the furnace, the saturated hydrocarbon is converted into an olefinic compound. For example, an ethane stream introduced into the cracking furnace is converted into ethylene and appreciable amounts of other hydrocarbons. A propane stream introduced into the furnace is converted to ethylene and propylene, and appreciable amounts of other hydrocarbons. Similarly, a mixture of saturated hydrocarbons containing ethane, propane, butane, pentane and naphtha is converted to a mixture of olefinic compounds containing ethylene, propylene, butenes, pentenes, and naphthalene. Olefinic compounds are an important class of industrial chemicals. For example, ethylene is a monomer or comonomer for making polyethylenes. Other uses of olefinic compounds are well known to those skilled in the art.
As a result of the thermal cracking of a hydrocarbon, the cracked product stream can also contain appreciable quantities of hydrogen, methane, acetylene, carbon monoxide, carbon dioxide, and pyrolytic products other than the olefinic compounds. At the furnace exit, the product stream is cooled to remove the heavier gases.
The carbon monoxide formed during the cracking of a hydrocarbon, if in excess quantity, can have a detrimental effect on downstream treatment process of the desired olefinic compound. For example, ethylene produced by thermal cracking of ethane generally is contaminated with small quantity of acetylene which is usually selectively hydrogenated to ethylene in a hydrogenation reactor. Carbon monoxide in excess quantity has been shown to significantly cool the temperature of the hydrogenation reactor thereby making the selective hydrogenation of acetylene considerably less effective.
During the thermal cracking process, a semi-pure carbon which is termed "coke" is also formed in the cracking furnace as a result of the furnace cracking operation. Coke is also formed in the heat exchangers used to cool the product stream flowing from the cracking furnace. In order to burn out the deposits of coke, a thermal cracking furnace is required to periodically shut down the furnace resulting in a substantial loss of production. Additionally, coke is a poor heat conductor. As coke is deposited, a higher furnace temperature is required to maintain the saturated hydrocarbon temperature in the cracking zone at a desired level resulting in increased fuel consumption and shorter furnace life.
Therefore, there is an ever-increasing need to improve the thermal cracking process by reducing the formation of carbon monoxide or coke, or both, during the cracking process. It would be a significant contribution to the art if an improved thermal cracking process were developed.